This invention relates to a water-repellent metal oxide film coated on a glass substrate and a method of forming the film. The film forming method belongs to the sol-gel process using a solution of a metal alkoxide or acetylacetonato. The water-repellent coating is suitable for application, for example, to architectural and vehicular window glasses to be exposed to rain water.
It is well known to coat a glass plate surface with a transparent, hard and abrasion-resistant film of a metal oxide such as, for example, oxide of silicon, titanium and/or zirconium. The metal oxide film can be formed by either a physical vapor deposition method or a sol-gel method using a solution of an organic metal compound such as alkoxide. When the coated glass plate is for use as an architectural or vehicular window glass often it is desired that the coating be repellent to water. However, with the conventional metal oxide coatings the contact angle of water drop hardly exceeds about 40 degrees.
JP 1-246160 A, which relates to an insulated glass panel constructed by confining dry gas between two opposite glass plates, mentions that a silicone coating film formed by the application of a silicon alkoxide solution exhibits water repellency. However, the water repellency of such a silicone film is only to a slight degree though it may be appreciable in respect of an antidimming effect.
JP 48-42350 shows to form a water-repellent film of a partially decomposed polyfluoroolefin by vacuum evaporation of poly(fluoroethylenepropylene). This film is formed of an organic material and hence is insufficient in durability and abrasion resistance particularly for outdoor uses.